1. Field of the Invention
The present invention relates to an apparatus for impregnating web-like material with thermally curable impregnating resin, comprising an impregnating trough in which the web-like material is brought into contact with the impregnating resin, an inlet line which leads to the impregnating trough and through which the impregnating resin is introduced into the impregnating trough, and a heating device which heats the impregnating resin.
2. Background Description
Apparatuses of this type are generally known in practice.
The impregnating of web-like material with thermally curable impregnating resin serves, together with the subsequent drying of the impregnated web-like material, for the production of impregnates, such as are used individually or in the form of a laminate formed from such impregnates; for example, for the coating of base members formed from wood material, for instance in the production of panels for cladding surfaces, for example, flooring.
As web material there comes into consideration not only in the state of the art but also in connection with the present invention, in particular, a composite formed from natural fibres and/or synthetic fibres, for example, a fabric, such as a woven fabric or a non-woven fabric, a mat, a textile, a roving, or the like.
Preferably, the web material is paper, the weight per unit area of which in the non-impregnated state can amount to between approximately 25 g/m2 and approximately 300 g/m2. As is well known, the paper layer of an impregnate which is intended to form a visual surface of the end product can be printed with a desired decoration.
In order to enable the impregnating resin to penetrate into the web material, the impregnating resin is mixed with a solvent, for example, water, the function of which is to lower the viscosity of the synthetic resin. If desired, further additives, for example, a curing agent, can be admixed with the resultant impregnating liquor. The already impregnated web material has to be dried before further processing, i.e. the solvent has to be removed from the impregnate so that of the impregnating liquor only the impregnating resin remains in the finished product.
If, in the context of the present invention, it is mentioned hereinafter that the web material is impregnated with impregnating resin or that impregnating resin penetrates into the web material, it is meant thereby that the web material is impregnated with impregnating liquor or that impregnating liquor penetrates into the web material, respectively. However, with regard to the end product, ultimately what matters is only that the impregnating resin has also penetrated the web material and remains therein during subsequent drying. Moreover, at this point it is to be noted that, although in the context of the present invention “the synthetic resin” or “the impregnating resin” is always referred to in the singular, this resin may also be a mixture of different synthetic resins.
As in any other industrially used process, also in the production of impregnates it must be endeavored to allow this process to proceed as rapidly and effectively as possible so as to keep as low as possible the cost component incurred thereby in the end product. For this purpose, it is of the utmost importance to enable the web-like material to be impregnated as rapidly and effectively as possible with the impregnating resin and subsequently dried. The time required for the impregnation, as is well known, becomes shorter as the viscosity of the impregnating liquor decreases. In order to achieve an as low as possible viscosity of the impregnating liquor, on the one hand, its solid content, i.e., resin content, can be lowered and, on the other hand, its temperature can be raised.
The solvent to be additionally added to reduce the viscosity in relation to a predetermined quantity of resin has to be removed again from the impregnated web-like material in the subsequent drying stage. This consumes energy and time, and thus, again contributes to an increase in the costs of the impregnate. Altogether, therefore, there is no cost advantage.
However, in practice, limits are also imposed on raising the temperature; in other words, the impregnating resin cures more rapidly at a higher temperature, i.e. polymerizes more rapidly. However, as the molecular weight of the resin increases, it penetrates to a lesser extent into the web-like material and the finished impregnate can subsequently be further processed to a lesser extent. For example, at a temperature of the impregnating trough of more than 35° C., the useful life of the liquor is reduced to such an extent that, in the event of an interruption in production, the impregnating liquor becomes unusable so quickly that it would be necessary to dispose of all the impregnating liquor present in the production plant, i.e., in particular in the impregnating trough. Of course, this cannot be tolerated.
Another problem which already arises in the state of the art at the trough temperatures of at maximum 35° C., is that because of high resin flow rates of up to 2,000 kg liquor/h the heat-exchanger surfaces of the impregnating trough have to be rather hot so as to enable the impregnating liquor accommodated in the impregnating trough to be brought to the desired trough temperature. Owing to the fact that, as a result of the geometrical configuration of the troughs, laminar flow regions naturally occur and in the most unfavorable cases even dead spaces are present, resin incrustations are formed time after time on the heat-exchanger surfaces, which in the course of time impair the heat transfer even further. A vicious circle is thereby instigated of ever-increasing necessary temperatures on the heat-exchanger surfaces and, accordingly, ever more rapidly occurring formation of incrustations—the trough “clogs up”.